Switching matrix release delay circuit

ABSTRACT

A multistage cross-point switching network is disclosed for use in a program controlled communication switching system. Each cross-point consists of a group of glass enclosed, sealed reeds around which are wound the operate and hold windings. The hold winding and a contact of the cross-point form a series path with the other cross-points of a network connection that is then held by appropriate potentials at each end. The network connection is released by interrupting this series path, along with the talking path conductors. To ensure that the talking conductors are interrupted first, the hold path includes a diode connected across the series path of cross-points to provide a current path to delay their release.

United States Patent Primary Examiner-Kathleen H. Claffy Assistant Examiner-Thomas W. Brown AnomeysCyril A. Krenzer, K. Mullerheim and B. E. Franz ABSTRACT: A multistage cross-point switching network is disclosed for use in a program controlled communication switching system. Each cross-point consists of a group of glass enclosed, sealed reeds around which are wound the operate and hold windings. The hold winding and a contact of the cross-point form a series path with the other cross-points of a network connection that is then held by appropriate potentials at each end. The network connection is released by interrupting this series path, along with the talking path conductors. To ensure that the talking conductors are interrupted first, the hold path includes a diode connected across the series path of crosspoints to provide a current path to delay their release.

LLF A-mArmx ja nlirem c MATRri D MA TRIX H TRUNK X-POlNT x-Pomr, x-pomr X-POINT HCI CONTROL CIRCUIT r 01 Fl F? F? l '7 F17 WRIT l 'Ew I l i T I r t 51:; H W? i F I s I To (:02 I l I l SUCCEEDING I E -s| l l l I y I EQUIPMENT w2 RING; l J, v I j, i

' /r T r l 1 l l 1 l I l 1 co AH i a i I i H I CH I DH D wl! Zr'u L] I L 1% Pl .rPULL p AG SR co C COMMON CONTROL PATENIEB AUB24 IQYI JOEPZOQ 202200 INVENTOR JOHANNES DRAAYER BY & pj- V ATTORNEY EVE;

P5553 ozammounm ok Eb P5950 6528 x23; 5oz

SWITCHING MATRIX RELEASE DELAY CIRCUIT BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to arrangements in switching system matrix controls for ensuring that the cross-point contacts are dry" i.e., no voltages present upon the reeds, such as could cause a current to flow upon the contacts mating; or no current flow through the contacts when they are separating, during the switching operations.

2. Description of the Prior Art As is known, relay cross-point switching systems employ switches, each made up of a coordinate array of relay contact sets. The cross-point switching contacts used in certain of these matrices are reed relays, wherein the contacts are sealed in glass containers and the relay winding is wound around all the envelopes of the contacts comprising the relay. Though providing many improved properties, the present dry-reed capsules are limited in their current carrying and especially in their current-breaking capabilities. Protection from excessive currents in the switch path and provisions for the dry switching of these contacts is highly desirable.

In these matrices, it is a common practice to include a separate winding on each cross-point for the purpose of holding the cross-point operated after it has been operated by the energizationof an operating winding. This separate winding is placed in series with the corresponding windings of all the other cross-points of a particular transmission path, which is then readily held by the application of a battery and ground potential to the ends of the path from the terminal circuits of the matrices. One of the series terminals may conveniently be left connected to a particular potential while the other end may be brought through contacts for circuit control purposes. To simplify the circuitry and otherwise facilitate the control operations it is desirable to have the same device, the path hold relay, complete the hold path and close the transmission path conductors. But, the occasions when the series hold path must be interrupted while the transmission path is carrying a current necessitates that the transmission path be interrupted initially followed by the interruption of the hold path to prevent the cross-point relays releasing before the control device has opened the transmission path. The obvious expedient is to have separate devices, usually relays, for initially breaking the talking path and then after a timed interval, open the series holding path. As is evident, this requires at least two relays, a timing circuit and separate command functions from the control equipment.

It is therefore an object of the present invention to provide apparatus for ensuring that the contacts of a matrix do not carry any current when they are released.

SUMMARY OF THE INVENTION According to the invention, the facilities include a device to maintain the current flow through the cross-point hold windings for a short interval after the series circuit is interrupted by the hold control device. In particular, the device is a diode connected to each hold conductor at a point between an end matrix and the control contacts. The other side of the diode and each hold conductor at the other end of the switching network are connected to the same source of potential. The diode is poled to be reverse biased when the control contacts are in the operated condition, and to complete a short circuit of the hold path when the control contacts are opened. The hold control relay opens the hold path contacts and talking conductor contacts, but the short circuit delays the release of the cross-point relays, which ensures that tee current in the talking conductors is interrupted first.

BRIEF DESCRIPTION OF THE DRAWING The above mentioned and other features and advantages of this invention and the manner of obtaining them will become more apparent and the invention itself will be best understood I by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying single sheet of drawing on which the invention is disclosed with For the particular illustrative embodiment of the invention described hereinafter, a four-stage network is chosen.

The four stages of the network are referred to as the A, B, C and D stages and are implemented with reed relay cross-point matrices. Each stage is made up of a coordinate array of relay contact sets of which there is one such contact set at each cross-point between a plurality of vertical multiples and a plurality of horizontal multiples, each such multiple comprising a number of conductors according to the number of physical connections required to be established through the array for a single communication path set up through it. For instance in a telephone exchange, each multiple may comprise conductors corresponding to the tip and ring wires of a subscribers line together with other conductors affording control connections required for holding purposes. Each contact set is controlled by a single relay.

By selective operation of the relays, a communication path can be established between a line terminals, which are connected to horizontal or vertical multiples of the switching arrays in the first switching stage, through the switching stages and the links between them, to the trunk terminals in the last of the switching states concerned.

The four stages of the network are grouped functionally as the line-link frame and the trunk-link frame. The line-link frame contains the A and B stages, while the trunk-link frame contains the C and D stages. The adjacent stages are interconnected by multiconductor paths called links, which extend between the multiples of the switching arrays of one stage and the switching arrays of the next stage.

The line-link frame and the trunk-link frame are interconnected by groups of links called the BC link group which are identified by the code combination the line-link frame and trunk-link frame with which they are associated. The links of the BC link group must connect the B matrices of each linelink frame to the C matrices of each trunk-link frame. Each line-link frame contains the A matrices and the B matrice. The outlets of the A matrices must be connected to the inputs of the B matrices. Each trunk-link frame has the inlets of the D matrices connected to the C matrices outlets by CD link groups. A marker pathfinder system utilizing a four-stage network of this type is disclosed in greater detail in U.S. Pat. No. 3,349,189 to John G. VanBosse.

Referring to the drawing the telephone station STl of tee exchange is connected to the switching office over telephone line L1 and is terminated there in both a line-link network LLP and in a line circuit LCl.

The line circuit LC consists of a ferrod sensing element F1 and a cutoff relay C0. The ferrod sensing element comprises a stick of ferrite material having control windings W1 and W0, an interrogate winding I1 and a sense winding S1, wound on it. A complete description of ferrod elements suitable for application here is disclosed in U.S. Pat. No. 3,245,157 issued to A. M. Guercio and H. F. May; and applications Ser. No. 545,451 of F. A. Risky filed Apr. 26, 1966 now U.S. Pat. No. 3,466,402 and J. G. VanBosse, Ser. No. 523,365 filed Jan. 27, 1966 now U.S. Pat. No. 3,461,365.

The line L1 tip conductor is connected in the conventional manner through cutoff relay contacts CO1 and control winding WI to ground potential, the ring conductor is connected through cutoff relay contacts CO2 and control winding W2 to battery potential.

The control windings are so connected that when a current path is completed by the telephone station being placed in the off-hook state, this is coupled through the ferrite stick F1 to the interrogate I1 and the sense S1 windings. When the line is off-hook the ferrod is saturated and a pulse in the interrogate winding will not be coupled to the sense winding.

The interrogate and sense windings of every line circuit ferrod are connected through a scanning distributor DI-l operating in synchronism with an address generator AG to connect a current generator CG to the interrogate winding and a sense register SR to the sense winding. The lines are interrogated in response to commands from the common control and the results of the interrogation are returned to the common control.

The Common Control" shown at the bottom of the FIGURE may be of the type disclosed in the Bell System Technical Journal, Sept. i964, Vol. XLIII, No. 5, parts I and 2. It is a centralized data processing machine that is employed to implement the various control functions of the system. It includes: the usual semipermanent memory for storing information pertaining to the calls and other operations of the system in progress, including the data relative to addresses of the lines and the switches of the matrix used in each call; a permanent memory for storing the system-operating programs and other less changeable data; and a logic or control unit for processing the instructions required for controlling the peripheral equipment, including the line scanners and the network control equipment designated as marker" in the drawing.

In the drawing a cross-point from each of the A, B, C and D matrices is shown for a path through the network from the telephone STl to the trunk circuits TRl through the hold control HC. The cross-points shown for the path of telephone STl through the matrices include the operate and hold magnets, control conductors as well as the contacts for the talking pair ofconductors. The magnets have two windings, a pull winding operated from the marker to set up a path as directed by the common control, and a hold winding that is used to hold the connection via a series path from the line circuit, through each of the cross-point hold magnet windings and contacts to the hold control relay H at the trunk end. The hold control HCl consists of a relay H operated from the marker via A to extend the talking pair of conductors TIp and RING at contacts H1 and H2 respectively through to the trunk circuit TRl and to apply at contacts H3 a holding potential to the matrix crosspoint hold winding path. This path extends from battery potential at the line circuit LCl cutoff relay CO terminal, through the cutoff relay winding, contacts AH and the hold winding of the A matrix cross-point relay, contacts BH and the hold winding of the B matrix cross-point relay, contacts CH and the hold winding of the C matrix cross-point relay, contacts DH and the hold winding of the D matrix cross-point relay to the hold control HCl where through the contacts H3 of the hold control relay H the current path is completed to ground potential.

The talking conductors TIP and RING terminate in the trunk circuit TRl battery feed relay BF for the direct current path, and through contacts BFl and BF2 of the battery feed relay BF the coupling capacitors C1 and C2 to succeeding equipment where the path is completed to other subscriber telephones or to required message processing equipment.

A matrix connection as above described is released from the subscriber end by the subscriber station goingon hook to open the circuit to relay BF. This condition is detected from the open contacts 8P3 by the ID circuit and communicated through the marker to the common control. The common control via the marker causes the 0G circuit to release the hold relay H to open the talking path contacts H1 and H2 and at contact H3 to open the circuit to the series hold path of the cross-point relays after which they release.

when the release is initiated from the trunk end of the connection, the common control is similarly signaled from the succeeding equipment and responds by a command to the 0G circuit to release relay H. But conditions in the matrices at this time are very different, since the TIP and RING contacts of each cross-point may be carrying a current if telephone STl is off-hook. Therefore, depending on factors such as relay adjustment tolerances, and the characteristics of the cross-point reed relays, it is possible for some of the individual reed relay contacts to open before the contacts H1 and H2 of the hold relay H. This is highly undesirable since not only is the life of these devices decreased when they are used to break currentcarrying circuits, but the contact resistance increases and they become less reliable. Therefore, provisions have to be made to prevent even the remote possibilities of these contacts breaking the current-carrying transmission circuit before it is opened by the hold relay H.

To prevent this early release of the matrix, use is made of the energy stored in the coils of the matrix cross-point relays. When the hold circuit to the cross-point relays is opened at contacts H3, the normal action of these relays is to release, That is, the magnetic field set up to maintain the reed contacts in a closed state collapses. This collapse results in the release of the energy stored in each cross-point and manifests itself as a voltage of opposite polarity to that which created it. The disclosure of the present invention utilizes this energy by completing a path whereby a current, caused by this voltage of the collapsing fields, may flow. This current path is completed through diode D1, which is poled to present a high impedance to the normal polarities present during the time that a connection is held, but presents a low impedance path to the current of the collapsing field. This induced current through the matrix, cross-points and diode D1 delays the release of the cross-points, and insures that the transmission path is interrupted by the hold relay H1 before it is interrupted at the cross-points.

From the foregoing, it will be apparent that applicants arrangement; of connecting a diode in the hold circuit to provide a discharge path for the collapsing field current of the cross-points, provides a simple and economical solution to the problem of insuring the dry switching ofthe matrix contacts.

Various changes and alternative implementations will now occur to those skilled in the art without departing from the spirit and scope of this invention.

WHAT IS CLAIMED IS:

1. In a circuit comprising a plurality of relays which complete a signal path via associated contacts, a series hold path for said relays including a winding of each of said relays between two terminals of a potential source, and a means for releasing said series relays and said signal path comprising a contact means and means for preventing the breaking of the signal path by the series relays before the signal path is interrupted by said means for releasing said series relays comprising a unidirectionally conductive device connected from said series hold path adjacent said means for releasing said series relays to a terminal of said potential source and poled to be normally nonconductive, whereby upon operation of said means for releasing said series path, the series relays release is delayed.

2. In a communication switching system of the type having a marker apparatus to select paths and establish connections between a first set of communication path terminals and a second set of communication path terminals through a plurality of switching stages arranged in tandem between terminals of the first set and terminals of the second set, each of said stages comprising a plurality of relays arranged in coordinate arrays, each relay having an operate winding and a hold winding, with a unidirectional device individual to each of said relays and connected in series with the operate winding thereof, at the coordinate points of each of said arrays, each relay having a normally open set ofits own contacts connected in series with its hold winding, there being links interconnecting adjacent stages, each link including communication path conductors, an operate conductor interconnecting the series combination of the operate winding and a unidirectional device, and a hold conductor interconnecting the series combination of the hold winding and normally open contacts of a relay in each of the adjacent stages, busy links having the hold path and the communication path contacts closed at each end and having an operating current flowing through said communication path and a holding current flowing through the hold windings from a given potential source and including: the combination comprising circuit release means having make contacts in the hold path and talking paths at one end of said connection, and another unidirectionally conductive device of said release means to open said make contacts, the relays of said coordinate arrays in each of said stages of a busy connection are held operated until the release means make contacts l connected from each hold conductor to the potential source 5 are complete y open poled to be normally nonconductive, whereby upon operation 

1. In a circuit comprising a plurality of relays which complete a signal path via associated contacts, a series hold path for said relays including a winding of each of saiD relays between two terminals of a potential source, and a means for releasing said series relays and said signal path comprising a contact means and means for preventing the breaking of the signal path by the series relays before the signal path is interrupted by said means for releasing said series relays comprising a unidirectionally conductive device connected from said series hold path adjacent said means for releasing said series relays to a terminal of said potential source and poled to be normally nonconductive, whereby upon operation of said means for releasing said series path, the series relays release is delayed.
 2. In a communication switching system of the type having a marker apparatus to select paths and establish connections between a first set of communication path terminals and a second set of communication path terminals through a plurality of switching stages arranged in tandem between terminals of the first set and terminals of the second set, each of said stages comprising a plurality of relays arranged in coordinate arrays, each relay having an operate winding and a hold winding, with a unidirectional device individual to each of said relays and connected in series with the operate winding thereof, at the coordinate points of each of said arrays, each relay having a normally open set of its own contacts connected in series with its hold winding, there being links interconnecting adjacent stages, each link including communication path conductors, an operate conductor interconnecting the series combination of the operate winding and a unidirectional device, and a hold conductor interconnecting the series combination of the hold winding and normally open contacts of a relay in each of the adjacent stages, busy links having the hold path and the communication path contacts closed at each end and having an operating current flowing through said communication path and a holding current flowing through the hold windings from a given potential source and including: the combination comprising circuit release means having make contacts in the hold path and talking paths at one end of said connection, and another unidirectionally conductive device connected from each hold conductor to the potential source poled to be normally nonconductive, whereby upon operation of said release means to open said make contacts, the relays of said coordinate arrays in each of said stages of a busy connection are held operated until the release means make contacts are completely open. 